Parison and blow molding method for bottle having undercut

ABSTRACT

A parison ( 110 ) for a container having a substantially constant wall thickness, the container having a base, a top edge defining a round opening, the top edge defining a plane which is not parallel to the plane of the base, a neck portion disposed at the same angle as the plane defined by the top edge, a front outer surface, and a rear outer surface having a lower portion and an upper portion. The parison comprises a cylindrical upper neck portion ( 140 ) having a cavity extending therethrough, the upper nock having a top surface ( 145 ) edge defining a top plane. The parison also has a hollow, elongated body portion ( 150 ) having a closed lower end ( 155 ) and an upper end ( 160 ), the lower body portion having a major axis extending in a direction parallel to the longitudinal axis of the cylindrical upper neck portion, and having a front wall ( 170 ) and a rear wall ( 175 ). The front wall is thicker than said rear wall. Also included in the invention is a method of producing a bottle ( 100 ) from the parison.

FIELD OF INVENTION

The invention relates to blow molding, and more specifically to a methodfor blow molding a bottle with an undercut shape and a parison used inthe blow molding of a bottle with an undercut shape.

BACKGROUND OF THE INVENTION

It is known to produce plastic (or resin-based) bottles by injectionblow molding. Injection blow molding comprises the steps of firstproducing an intermediate resin article having a shape similar to thatof the final resin article. This intermediate resin article is oftenreferred to as the parison, or preform. The parison is usually formed byan injection molding process whereby molten resin is forced into acavity defined by the space between a moveable core rod and the parisonmold into which the core rod is placed. Once the injection molding partis complete, the thus-formed parison is transferred from the parisonmold to the blow mold via the moveable core rod on which it rests.

The parison is next transferred, via the core rod, to the blow mold. Thelongitudinal axis of the core rod is generally parallel to the plane ofseparation of the blow mold halves. The blow mold cavity has the shapeof the outside of the final bottle product. The parison is theninflated, often through the introduction of air through the core rod,and caused to expand to the shape of the blow mold. Typically, becausethe parison wall is effectively stretched during the blowing process,the final product wall thickness is less than the wall thickness of theparison.

The blow mold is typically comprised of two halves, each of which movesin a substantially opposite direction with respect to the other. Thecontact area where the two mold halves meet and later part (after theblowing is complete) is usually called the parting line. The partingline is usually substantially parallel to the longitudinal axis of thecore rod. Where special product shapes are desired, however, it issometimes necessary to have a parting line that is not linear orcompletely parallel to the core rod axis.

Where special bottle shapes are desired, and thus the parting line isnot linear, it becomes important to insure that the core rod can be bothtransferred into the location between the open blow mold halves andremoved from the same position with the blown bottle in place on thecore rod. Because of conventional machinery, it is equally important isthat the blown bottle be able to be stripped from the core rod in adirection parallel to the longitudinal axis of the core rod.

Because the blown bottle must be stripped from the core rod in adirection parallel to the axis of the core rod, it can be difficult toblow mold bottles having an undercut shape. This is especially truewhere it is important that the product bottle have a consistent wallthickness throughout. Where consistent wall thickness is desired, it ispreferred that the parison be positioned in (or as close as possible to)the geometric center of the blow mold cavity. Where the parison is notin the middle of the blow mold cavity, the distance that the moltenplastic comprising the parison must travel when blown is greater in someparts of the mold than in others. This incongruity in the distancestretched results in a bottle having varying wall thickness in itsdifferent regions.

SUMMARY OF INVENTION

The present invention provides both a method and a device for the blowmold production of a bottle having an undercut surface and an off-centervertical axis. The method involves the blow molding of a containerhaving a substantially constant wall thickness, but having an oblongbase, a round top edge defining a round opening, the round top edgedefining a plane which is not parallel to the plane of the base, a neckportion disposed at the same angle as the plane defined by the top edge,a front outer surface, and a rear outer surface having a lower portionand an upper portion. The method comprises the steps of forming aparison having a cylindrical upper neck portion having a cavityextending therethrough, the upper neck having a top surface edgedefining a top plane. The parison has a hollow, elongated lower bodyportion having a closed lower end and an upper end, the lower bodyportion having a major axis extending in a direction parallel to thelongitudinal axis of the cylindrical upper neck portion. The parisonalso has a front wall and a rear wall, the closed lower end defining aplane which is parallel to the top plane defined by the top surfaceedge. Below the top is a transition region connecting the upper neckportion and the lower body portion, the transition region having a topend with the same cross section as the cylindrical upper neck portionand a lower end with the same cross section as the upper end of thelower body portion. Important in this method is the fact that the frontwall is thicker than the rear wall. After the parison is made accordingto these characteristics, it is blow molded in a blow mold to form thefinal product shape.

The invention also comprises the parison itself. The parison of theinvention has a first wall a first distance from the blow mold innersurface and a second wall a second distance from the inner surface. Thefirst distance is less than the second distance and the first wall isthinner than the second wall. The parison comprises a cylindrical upperneck portion having a cavity extending therethrough, the upper neckhaving a top surface edge defining a top plane. The parison also has ahollow, elongated lower body portion having a closed lower end and anupper end, the lower body portion having a major axis extending in adirection parallel to the longitudinal axis of the cylindrical upperneck portion. The lower body portion has a front wall and a rear walland a closed lower end defining a plane which is parallel to the topplane defined by the top surface edge. The parison also has a transitionregion connecting the upper neck portion and the lower body portion, thetransition region having a top end with the same cross section as thecylindrical upper neck portion and a lower end with the same crosssection as the upper end of the lower body portion. The transitionregion has a sloped wall extending from the rear wall of the lower bodyportion out and up from the rear wall of the lower body portion to theupper neck portion. The front wall is thicker than the rear wall. Thisparison produces a bottle having a parting line mark on its sides, asopposed to its front or rear walls, which is generally moreaesthetically pleasing.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, but are notrestrictive, of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawing. It is emphasizedthat, according to common practice, the various features of the drawingare not necessarily to scale. On the contrary, the dimensions of thevarious features are arbitrarily expanded or reduced for clarity.Included in the drawing are the following figures:

FIG. 1 is a schematic view of a bottle blow molded in accordance withthe present invention;

FIG. 2 is a schematic view of a blow mold which would not work withtypical core rod handling apparati;

FIG. 3 is a cross-sectional sideview of a parison mold according to thepresent invention;

FIG. 4 is top view of the bottom half of the parison mold of FIG. 3;

FIG. 4A shows an isometric view of a parison mold bottom half;

FIG. 5 is a cross-sectional sideview of the parison mold of FIG. 3 witha core rod in place;

FIG. 6 is a cross-sectional sideview of the parison mold of FIG. 3 witha core rod inserted and a resin injection nozzle in place;

FIG. 6A is a cross-sectional sideview of the apparatus of FIG. 6 showingthe injection of resin to form the parison;

FIG. 7 is a cross-sectional sideview of a blow mold according to thepresent invention;

FIG. 7A shows an isometric view of a blow mold bottom half;

FIG. 8 is a top view of the bottom half of the blow mold of FIG. 7;

FIG. 9 is a bottom view of the top half of the blow mold of FIG. 7;

FIG. 10 is a cross-sectional sideview of the blow mold of FIG. 7 with acore rod and parison disposed therein;

FIG. 11 is a schematic sideview of a core rod and parison disposedwithin a blow mold according to the present invention;

FIGS. 11A and 11B are sections taken from FIG. 11; and

FIGS. 12A and 12B are the sections of FIGS. 11A and 11B, respectively,with dimensions indicated thereon.

DETAILED DESCRIPTION OF INVENTION

The present invention relates to the production of a bottle having anoff-center vertical axis. FIG. 1 shows one example of the type of bottle100 having an undercut region 110 which can be produced through a blowmolding process according to the present invention. Before the presentinvention, this type of bottle was typically made through an extrusionmolding process because its shape presented several problems toconventional blow-molding techniques.

FIG. 2 shows a mold shape which would provide product bottle 100 of FIG.1. Typically, the parison shape for a bottle of constant wall thicknesshas itself a constant wall thickness. Such a parison is then insertedinto the geographic center (or near geographic center) of the blow moldto insure consistent wall thickness. In the case of the bottle of FIG.1, this parison would have to be oriented approximately as shown in FIG.2, with core rod 200 and parison 210 in place within the near geographiccenter of the mold. The problem with this requirement, however, is thatconventional processing machinery strips the product bottle from thecore rod in a direction parallel to the longitudinal axis of the corerod. Thus, the resultant blown bottle of FIG. 2 cannot be stripped fromthe core rod in a direction parallel to the axis of the core rod becausethe front part of the bottle blocks its removal. An entirely new machinefor moving the core rod in an articulated fashion with respect to thebottle during the stripping step would have to be created which wouldcantilever the core rod with respect to the blown bottle. Moreover, atraditional machine for stripping the bottle from the core rod could notbe used.

One alternative to this problem would be to orient the blow mold withrespect to the core rod such that the product bottle is rotated 90° fromthat shown in FIG. 7. This would result, however, in the parting line(which is visible on the product bottle) being oriented on the front andback faces of the bottle, rather than on the sides. In addition to beingless aesthetically pleasing, the front/back parting line makes labeladhesion more difficult.

The present invention solves these problems by providing a novel methodand parison. The parison used in the present invention has varying wallthickness along its different sides which overcome the need for theparison to be present in the physical middle of the blow mold. The useof this novel parison allows undercut bottles of the type shown in FIG.1 to be blow molded, whereas in the past extrusion molding would likelyhave been used.

FIG. 3 shows a cross-sectional sideview of the parison mold according tothe present invention. FIG. 3 shows parison mold 305 with parison moldtop half 300 and parison mold bottom half 310 which come together alongnon-linear parting line 320 to form parison mold cavity 330. FIG. 4shows a top view of parison mold bottom half 310 having cavity 450. FIG.4A shows an isometric view of the bottom half 310.

FIG. 5 shows a schematic view of the cross-sectional sideview of parisonmold 305 shown in FIG. 3 with core rod 500 oriented between mold halves300 and 310. When the mold closes, both core rod 500 and top mold half300 move toward mold half 310 as shown by the arrows in FIG. 5.Alternatively, all three components could move as the mold closes. FIG.6 shows core rod 500 in place within parison mold cavity 330. Also shownschematically is resin injection nozzle 600 which delivers resin intoparison mold cavity 330. FIG. 6A shows the space defined between corerod 500 and parison mold cavity 330 being filled with resin to form aparison. As will be discussed more fully below, core rod 500 with itspartially cooled resin will be moved to the blow mold cavity.

FIG. 7 shows a cross-sectional sideview of a blow mold 705 that can beused in the present invention. Blow mold top half 700 contacts blow moldbottom half 710 along blow mold parting line 720 to form blow moldcavity 730. FIG. 7A shows an isometric view of blow mold bottom half710. FIG. 8 shows a top view of blow mold bottom half 710 having cavity810, FIG. 9 shows a bottom view of blow mold top half 700 having cavity910.

FIG. 10 illustrates a schematic cross-sectional side view of blow mold705 shown in FIG. 7, with core rod 500 and parison 610 disposed withinblow mold cavity 720. In this position, the parison is ready to beblown, according to known practices, and air is injected through a smallpassageway within core rod 500 (not shown) which blows the parisonoutward against the blow mold inner wall.

FIG. 11 shows a more detailed view of a parison 110 disposed on core rod120. This embodiment is slightly different than those shown in the abovefigures, but is consistent with the present invention. Specifically,parison 110 comprises a cylindrical upper neck portion 140 having acavity extending therethrough. Upper neck portion 140 has a top surfaceedge 145 defining a top plane, a hollow, elongated lower body portion150 having a closed lower end 155 and an upper end 160. Lower bodyportion 150 has a major axis extending in a direction parallel to thelongitudinal axis of the cylindrical to upper neck portion 140, and hasa front wall 170 and a rear wall 175. Closed lower end 155 defines aplane which is parallel to the top plane defined by the top surface edge145. Also shown in FIG. 11 is a transition region 180 connecting upperneck portion 140 and lower body portion 150. Transition region 180 has atop end 181 with the same cross section as the cylindrical upper neckportion 140 and a lower end 182 with the same cross section as the upperend 160 of lower body portion 150. Transition region 180 has a slopedwall extending from rear wall 175 of lower body portion 150 out and upfrom rear wall 175 to upper neck portion 140.

As can be seen in FIG. 11, front wall 170 is thicker than the rear wall175. Sections A—A and B—B are shown in FIGS. 11A and 11B, respectively.FIG. 11A shows a cross-section of lower body portion 150 near upper end160. FIG. 11B shows a cross-section of lower body portion 150 toward theclosed lower end 155. FIG. 11A shows the cross-section where thedistance from the parison to the blow mold wall is approximately thesame on either side of the parison. In contrast, FIG. 11B shows thecross-section where the distance from the parison to the blow mold wallis much greater on front wall 170 of the parison than on rear wall 175.Where the distance is greater, the thickness of the parison itself isalso greater.

This change in parison wall thickness is dependent upon the distance theparison wall material must travel when blown. In those areas along theparison wall where little stretching will occur, there exists no need tosupply extra material. On the other hand, in those areas along theparison wall where a relatively large amount of stretching will occur,additional material is needed.

FIGS. 12A and 12B illustrate a preferred embodiment of the parison shownin FIG. 11. In FIG. 12A, x=about 0.08 inches (“about” meaning +/−0.01inches, in all cases herein unless otherwise noted), and y=about 0.07inches. In FIG. 12B, x′=about 0.17 inches, and y′=about 0.07 inches.

Also illustrated in FIGS. 11 and 12 is the fact that along front wall170 of the parison the wall thickness is tapered from closed lower end155 having a first thickness up to a thickest central portion and downto a second thickness at the transition region. At the lower end oftransition region 182 at front wall 170, the parison wall thickness isabout equal to the parison wall thickness at the upper end 160 of lowerbody portion 150. This is because the distance that the materialcomprising the parison at that point must travel during blowing is aboutthe same.

This parison also relates to a novel method of blow molding a containerhaving an undercut shape. More specifically, the method according to thepresent invention provides a bottle having an undercut shape having asubstantially constant wall thickness. The bottle also has a base, around top edge defining a round opening, the round top edge defining aplane which is not parallel to the plane of the base, a neck portiondisposed at the same angle as the plane defined by the top edge, a frontouter surface, and a rear outer surface having a lower portion and anupper portion. The method used to blow mold such a bottle comprises thesteps of first forming a particular parison, as discussed above, andthen blowing the parison in a blow mold. The parison has a first wallwhich is a first distance from the blow mold inner surface and a secondwall which is a second distance from the inner surface of the blow mold.The first distance is less than the second distance and the first wallis thinner over most of its length than the second wall.

More specifically, the method uses a parison where the front wall isabout 2.5 times thicker at its thickest point than the rear wall. Thisaspect of the invention is important as the material along the frontwall must travel much farther during blowing, and thus is stretched to amuch greater extent, than the material comprising the rear wall of theparison.

Although illustrated and described herein with reference to certainspecific embodiments, the present invention is nevertheless not intendedto be limited to the details shown. Rather, various modifications may bemade in the details within the scope and range of equivalents of theclaims and without departing from the spirit of the invention.

1. A method of blow molding a container having substantially constantwall thickness and an outside shape with a non-linear parting line, themethod comprising the steps of: placing a parison into a blow moldhaving an inner surface which is the shape of the outside of saidcontainer being molded, said parison having a first wall a firstdistance from said blow mold inner surface and a second wall a seconddistance from said inner surface wherein said first distance is lessthan said second distance and said first wall is thinner than saidsecond wall; and blowing said parison in said blow mold, without firststretching said second wall, into said container.
 2. The method of claim1 wherein said parison has: a cylindrical upper neck portion having acavity extending therethrough, said upper neck having a top surface edgedefining a top plane; a hollow, elongated lower body portion having aclosed lower end and an upper end, said lower body portion having amajor axis extending in a direction parallel to the longitudinal axis ofsaid cylindrical upper neck portion, and having a front wall and a rearwall, said closed lower end defining a plane which is parallel to saidtop plane defined by said top surface edge; and a transition regionconnecting said upper neck portion and said lower body portion, saidtransition region having a top end with the same cross section as saidcylindrical upper neck portion and a lower end with the same crosssection as said upper end of said lower body portion, said transitionregion having a sloped wall extending from the rear wall of said lowerbody portion out and up from said rear wall of said lower body portionto said upper neck portion.
 3. The method of claim 2 wherein said slopedwall is thicker than said rear wall.
 4. The method of claim 1 whereinsaid front wall is about 2.5 times as thick as said rear wall.
 5. Themethod of claim 2 wherein said front wall thickness is tapered from saidclosed lower end having a first thickness up to a thickest centralportion and down to a second thickness at said transition region whereinsaid first thickness and said second thickness are about equal.
 6. Themethod of claim 2 wherein said sloped wall is tapered from the rear wallof said lower body portion having a first thickness up to a thickestcentral portion of said sloped wall and down to a second thickness atsaid cylindrical upper neck portion.
 7. A parison for a container havingsubstantially constant wall thickness, said container having a base, atop edge defining a round opening, the top edge defining a plane whichis not parallel to the plane of the base, a neck portion disposed at thesame angle as the plane defined by the top edge, a front outer surface,and a rear outer surface having a lower portion and an upper portion,the parison comprising: a cylindrical upper neck portion having a cavityextending therethrough, said upper neck having a top surface edgedefining a top plane; a hollow, elongated body portion having a closedlower end and an upper end, said lower body portion having a major axisextending in a direction parallel to the longitudinal axis of saidcylindrical upper neck portion, and having a front wall opposite a andrear wall; wherein said front wall is thicker than said rear wall. 8.The parison of claim 7 wherein said front wall is about 2.5 times asthick as said rear wall.
 9. The parison of claim 7 wherein said frontwall thickness is tapered from said closed lower end having a firstthickness up to a thickest central portion and down to a secondthickness at said transition region wherein said first thickness andsaid second thickness are about equal.
 10. A parison for a containerhaving substantially constant wall thickness, said container having anoblong base, a round top edge defining a round opening, the round topedge defining a plane which is not parallel to the plane of the base, aneck portion disposed at the same angle as the plane defined by the topedge, a front outer surface, and a rear outer surface having a lowerportion and an upper portion, the parison comprising: a cylindricalupper neck portion having a cavity extending therethrough, said upperneck having a top surface edge defining a top plane; a hollow, elongatedlower body portion having a closed lower end and an upper end, saidlower body portion having a major axis extending in a direction parallelto the longitudinal axis of said cylindrical upper neck portion, andhaving a front wall opposite a rear wall, said closed lower end defininga plane which is parallel to said top plane defined by said top surfaceedge; and a transition region connecting said upper neck portion andsaid lower body portion, said transition region having a top end withthe same cross section as said cylindrical upper neck portion and alower end with the same cross section as said upper end of said lowerbody portion, said transition region having a sloped wall extending fromthe rear wall of said lower body portion out and up from said rear wallof said lower body portion to said upper neck portion; wherein saidfront wall is thicker than said rear wall.
 11. The parison of claim 10wherein said sloped wall is thicker than said rear wall.
 12. The parisonof claim 1 wherein said front wall is about 2.5 times as thick as saidrear wall.
 13. The parison of claim 10 wherein said front wall thicknessis tapered from said closed lower end having a first thickness up to athickest central portion and down to a second thickness at saidtransition region wherein said first thickness and said second thicknessare about equal.
 14. The parison of claim 10 wherein said sloped wallhas a thickness greater than said rear wall.
 15. The parison of claim 10wherein said sloped wall is tapered from the rear wall of said lowerbody portion having a first thickness up to a thickest central portionof said sloped wall and down to a second thickness at said cylindricalupper neck portion.